Conventionally, there has been proposed an internal EGR control device of this kind in Patent Literature 1. In this internal EGR control device, the amount of internal EGR caused to remain in cylinders is controlled by changing an intake cam phase and an exhaust cam phase with respect to a crankshaft by a variable intake cam phase mechanism and a variable exhaust cam phase mechanism, respectively, and by changing the lift of an intake valve by a variable intake lift mechanism. Specifically, the opening and closing timing of intake and exhaust valves is controlled by controlling the above-mentioned variable intake/exhaust cam phase mechanisms and the variable intake lift mechanism depending on operating conditions of the engine which are determined e.g. according to the rotational speed of the engine and the opening of a throttle valve.
As described above, in the conventional internal EGR control device, the internal EGR amount is controlled only by controlling the opening and closing timing of the intake and exhaust valves depending on the operating conditions, such as a rotational speed and a throttle valve opening, of the engine. However, even when the operating conditions of the engine are the same, if the actual opening and closing timing of the intake and exhaust valves or the like varies due to aging, a state and properties of burned gases, e.g. the amount and temperature of burned gases change, and accordingly, the temperature within each cylinder immediately before the start of the compression stroke also changes. This sometimes makes it impossible for a conventional internal EGR control device to properly control the temperature within the cylinder, and in this case, the state of combustion becomes unstable.
The present invention has been made to provide a solution to the above-described problems, and an object thereof is to provide an internal EGR control device for an internal combustion engine, which, even when a change in the actual valve timing of exhaust valves is caused by aging, is capable of properly controlling an internal EGR amount while compensating for an adverse influence caused by the change, and thereby properly controlling the temperature within the cylinder.
[Patent Literature 1]    Japanese Laid-Open Patent Publication (Kokai) No. S62-10411